diff --git a/storages/backends/sftpstorage.py b/storages/backends/sftpstorage.py
index f07e8cf5d..4b4194828 100644
--- a/storages/backends/sftpstorage.py
+++ b/storages/backends/sftpstorage.py
@@ -49,6 +49,7 @@ def __init__(self, host=None, params=None, interactive=None, file_mode=None,
         # for now it's all posix paths.  Maybe someday we'll support figuring
         # out if the remote host is windows.
         self._pathmod = posixpath
+        self._sftp = None
 
     def _connect(self):
         self._ssh = paramiko.SSHClient()
@@ -79,13 +80,13 @@ def _connect(self):
         except Exception as e:
             print(e)
 
-        if not hasattr(self, '_sftp'):
+        if self._ssh.get_transport():
             self._sftp = self._ssh.open_sftp()
 
     @property
     def sftp(self):
         """Lazy SFTP connection"""
-        if not hasattr(self, '_sftp'):
+        if not self._sftp or not self._ssh.get_transport().is_active():
             self._connect()
         return self._sftp
 
diff --git a/tests/test_sftp.py b/tests/test_sftp.py
index 754e98703..5b9c01c75 100644
--- a/tests/test_sftp.py
+++ b/tests/test_sftp.py
@@ -2,6 +2,7 @@
 import stat
 from datetime import datetime
 
+import paramiko
 from django.core.files.base import File
 from django.test import TestCase
 from django.utils.six import BytesIO
@@ -133,6 +134,24 @@ def test_url(self):
             self.storage._base_url = None
             self.storage.url('foo')
 
+    @patch('paramiko.transport.Transport', **{
+        'is_active.side_effect': (True, False)
+    })
+    @patch('storages.backends.sftpstorage.SFTPStorage._connect')
+    def test_sftp(self, connect, transport):
+        self.assertIsNone(self.storage.sftp)
+        self.assertTrue(connect.called)
+        connect.reset_mock()
+        self.storage._ssh = paramiko.SSHClient()
+        self.storage._ssh._transport = transport
+
+        self.storage._sftp = True
+        self.assertTrue(self.storage.sftp)
+        self.assertFalse(connect.called)
+
+        self.assertTrue(self.storage.sftp)
+        self.assertTrue(connect.called)
+
 
 class SFTPStorageFileTest(TestCase):
     def setUp(self):